This invention relates to a unique system for controlling an air compressor and an air dryer as used in a vehicle's air brake system, which avoids unnecessary purging of the air dryer under certain pre-determined conditions.
One of the various braking systems used by heavy vehicles, is a compressed air brake system. This system typically includes an air compressor, which receives air from an engine intake manifold or air filter, an air dryer, a reservoir, and a governor that controls the operating mode of the air compressor. The air compressor operates in one of two modes, a loading or compressing mode and a unloading mode. When the pressure level in the reservoir falls below a specified minimum level, the governor causes the air compressor to operate in the compressing mode. When the air compressor is in the compressing mode it compresses air received from the engine intake manifold and sends it through a pneumatic line to the air dryer. The air dryer includes a filter that removes moisture and contaminants from the air, which is then sent to the reservoir. The air from the reservoir is used to supply air pressure to the vehicle's brakes.
Once the pressure level in the reservoir reaches a specified maximum pressure, the governor causes the air compressor to cut-out and operate in the unloading mode. In this mode, air is no longer supplied to the brake system. Also during this mode, air is purged from the air dryer causing moisture to be removed from the filter and discharged to the atmosphere. This purging will continue until a pre-set pressure level in the reservoir is reached or a fixed volume of air is exhausted, dependant on the type of air dryer.
Prior art systems control both the compressor and air dyer purge valve with the same pneumatic signal. Hence, each time the compressor unloads, the air dryer is purged. It would be advantageous to have separate controls for the compressor and the dryer such that when the engine is not being fueled, i.e. the driver is not pressing down on an accelerator pedal, the compressor would provide compressed air to the reservoir when the reservoir pressure is above cut-in but below cut-out pressure, without adding to parasitic engine power loss. To accomplish this it is necessary to control the air dryer purge independently from the compressor by solely monitoring the reservoir pressure.
Thus, it is desirable to have an air braking control system that continuously monitors the fueling status of the engine and the air pressure in the reservoir so that unnecessary purging of the air dryer is avoided under certain pre-determined conditions.